The present invention relates to methods for fabricating semiconductor devices, and more particularly relates to semiconductor device fabrication methods which enable semiconductor light emitters, such as semiconductor laser devices, to be mounted in a self-aligned manner.
Typical digital-versatile-disc (hereinafter referred to as “DVD”) players and recorders need to have the capability of playing back not only DVDs but also compact discs (hereinafter referred to as “CDs”), and also have to include the capability of reproducing, and storing data on, recordable CDs (CD-Rs) which have become widespread rapidly in recent years.
As light for reproducing DVDs, a red laser beam with a wavelength in the 650 nm band is employed, while an infrared laser beam with a wavelength in the 780 nm band is used as light for playing back CDs and CD-R discs. Thus, in the currently available DVD players and recorders, two semiconductor laser diodes are incorporated in the form of an array: a red semiconductor laser diode for generating a red laser beam and an infrared semiconductor laser diode for generating an infrared laser beam.
With an increasing demand for smaller information equipment such as personal computers, DVD players and recorders also need to be further reduced in size and thickness. To that end, it is indispensable to decrease the size and thickness of optical pickups. A method for reducing the size and thickness of an optical pickup is to simplify an optical system.
As one method for simplifying an optical system, integration of a red semiconductor laser diode and an infrared semiconductor laser diode is considered. The current DVD players and recorders include two types of optical system components for a red semiconductor laser diode and an infrared semiconductor laser diode. Integration of the two semiconductor laser diodes, that is, the red and infrared semiconductor laser diodes, allows an optical system component to be shared, thereby realizing an optical pickup of smaller size and thickness.
For instance, as one example of the integration of a red semiconductor laser diode and an infrared semiconductor laser diode, a so-called monolithic semiconductor laser diode array integrated on a single substrate is disclosed in Japanese Laid-Open Publication No. 11-186651.
Also, Japanese Laid-Open Publication Nos. 11-144307 and 11-149652 disclose other examples of an optical pickup, in which optical-system-component sharing is achieved by hybrid integration of two semiconductor laser chips for a red laser and an infrared laser.
Nevertheless, in the conventional monolithic two-wavelength laser diode array, active layers of the respective laser diodes have different compositions and thus have to be grown in different process steps, which results in the problem of low yields. In particular, when high-output laser diodes are monolithically integrated, yields decrease significantly.
Moreover, it is very difficult, from the viewpoint of crystal growth, to monolithically integrate a gallium nitride (GaN)-based blue laser diode, which is used in high density DVDs, and an aluminum gallium indium phosphide (AlGaInP)-based red laser diode.
The conventional hybrid optical pickup, on the other hand, have the problem that when the red semiconductor laser chip and the infrared semiconductor laser chip are assembled using assembly equipment, it is difficult to adjust and optimize the locations of the active layers of, and the distance between the light emitting points of, the semiconductor laser chips.
In recent years, a mounting method in which a fluidic self-assembly technique is used has been developed as one type of device-mounting method.
In the fluidic self-assembly technique, devices (hereinafter referred to as “function blocks”) ranging in size from 10 μm to several hundred μm and having a given shape are spread in a liquid to form a slurry. The liquid (suspension) in the form of slurry is poured over the surface of a substrate of, e.g., silicon having recessed portions therein. The recessed portions are substantially the same as the function blocks in terms of size and shape. In this manner, the function blocks spread in the liquid are placed in the recessed portions and thereby mounted onto the substrate.
However, the conventional fluidic self-assembly process has a drawback in that it is not easy to form in the substrate the recessed portions into which the function blocks are inserted, which results in low productivity.